EECS Colloquium

                                                                                                                        Host: Dong-Seon Lee / Language: English

Friday, April. 4, 2025, 14:30~

Haerim Hall, EECS-B Bldg. 1st Floor

 Semiconductor epitaxy without chemical bonds on wafer

for 3d hetero-integration technology 

Prof. Young Joon Hong

Department of Nano Engineering, Department of Nano Science and Technology, SKKU 

Advanced Institute of Nanotechnology (SAINT), and Department of Display Engineering, Sungkyunkwan University

 
[Abstract]                                                                                                                                                                                                                                                                                                                                                                                                                     

  Glasses-type augmented reality (AR) displays demand extremely advanced display technologies, requiring not only ultra-high resolution (>2,000 ppi or >60 pixels per degree), and high brightness (>hundreds of thousands of nits), but also compliance with defect pixel standards (ISO 9241). Among various flat panel display platforms (LCD, OLED, LED, etc.), micro-LEDs stand out as the most promising solution. However, one of the major technological hurdles for commercialization is the mechanical transfer accuracy required for ultra-high-density pixel arrays, which must be withinsub-100 nm—a significant challenge. Current mini-LED displays (with sub-pixel sizes ~50 µm) use precise chip transfer or alignment-and-bonding techniques to position patterned chip arrays onto backplane circuits. Even with the most advanced mechanical transfer methods, the alignment error is still around 1 micron. While this level of accuracy is acceptable for large-pixel displays like TVs, it is insufficient for AR displays requiring micro-LED chips smaller than 5 µm. Therefore, a new pixel integration approach is essential.Epitaxy is a key technology for producing high-quality single-crystalline LED thin films. However, conventional epitaxy forms strong chemical bonds between the substrate and epitaxial layers, making it difficult to release the layers uniformly (e.g., laser lift-off or time-consuming chemical ift-off methods). Also, chip-level patterning is implemented first, then the as-deployed chip arrays are transferred to carrier substrates or bonded to the surface of interest. In this process, state-of-the-art mechanical alignment is insufficient for AR display applications. In this lecture, we introduce non-covalent epitaxy techniques—specifically, remote epitaxy and van der Waals epitaxy—which enable the growth of epitaxial layers without forming strong chemical bonds with the substrate. Utilizing these methods, we demonstrate the fabrication of ultra-high-density, vertically stacked R/G/B micro-LED pixels, achieved through microelectronics processing with exquisitely fine patterning and alignment. We will also discuss the fundamental principles of remote and van der Waals epitaxy. The results presented here represent not only a breakthrough for ultra-high-resolution inorganic emissive displays, but also a foundational methodology for the future of 3D heterogeneous integration in electronic device

Related publications:

1.    "Roles of Nanoscale Defects of Graphene in Remote Epitaxy of GaN" Small (submitted).

2.    "Remote epitaxial interaction through graphene" Sci. Adv. 9, adj5379 (2023).

3.    "Exceptional thermochemical stability of graphene on N-polar GaN for remote epitaxy" ACS Nano 17, 21678 (2023).

4.    "Vertical full-colour micro-LEDs via 2D materials-based layer transfer" Nature 614, 81 (2023).

5.    "Remote Epitaxy" Nat. Rev. Methods Primers 2, 40 (2022).

6.    "Remote heteroepitaxy of GaN microrod heterostructures for deformable light-emitting diodes and wafer recycle" Sci. Adv. 6, eaaz5180 (2020). 

[Short Biography]

 Dr. Hong received his B.S. degree from Korea University in 2004 and his Ph.D. from Pohang University of Science and Technology (POSTECH) in 2011, all in Materials Science and Engineering. From 2011 to 2012, he was a JSPS (Japan Society for the Promotion of Science) Foreign Researcher Fellow at the Research Center for Integrated Quantum Electronics, Hokkaido University, Japan. He served as a professor in the Department of Nanotechnology and Advanced Materials Engineering at Sejong University from 2012 to 2024. He is currently a professor at the SKKU Advanced Institute of Nanotechnology (SAINT) and the Department of Display Engineering at Sungkyunkwan University, Korea